Chapter 3. Carbon and nutrient balances in three mountain oases of Oman
3.6 Conclusions
Chapter 3: Carbon and nutrient balances in three mountain oases of Oman
Annual apparent NUE was much higher in annual crops than in perennials.
Similar to our results, data obtained from 197 countries indicated average use efficiencies of 50% for N, 40% for P, and 75% for K (Sheldrick et al., 2002). The lower NUE of the perennial trees compared to garlic was largely due to much lower nutrient outputs in fruit production. However, calculation of the annual apparent NUE in perennial trees based on harvested yield does not take into account total nutrient uptake and storage by the trees (Hedlund et al., 2003). The high K uptake by garlic crops raise questions about soil K sources. Further investigations can play an important role in assessing the effect of soil K depletion on long-term crop production.
The reliability of our total C balances is severely hampered by the lack of reliable data on root C contributions which has been the subject of much recent research (Kuzyakov et al., 2001; Kuzyakov, 2002; Werth and Kuzyakov, 2008; Pumpanen et al., 2009). From their comprehensive studies under controlled conditions Kuzyakov and Larionova (2006) concluded that root respiration contributed approximately 40% to the total CO2 efflux from soils. Kelting et al. (1998) have partitioned soil respiration into: (1) 32% as a root respiration, (2) 20% as microbial respiration in the rhizosphere, and (3) 48% as root free soil respiration (basal respiration). A recent study (Atarashi-Andoh et al., 2011) on the partitioning of soil heterotrophic and autotrophic respiration using 14C concluded that about 31-39% of the total CO2 efflux from the soil were from root-derived C. Such isotope studies would be necessary to trace the fate of the assimilated C by annual and perennial trees in agroecosystems such as ours.
Acknowledgement
We thank the farmers of Al Jabal Al Akhdar and the Agricultural Extension Centre of the Ministry of Agriculture and Fisheries at Sayh Qatanah (Oman) who supported this research infrastructurally. We are also thankful to Eva Wiegard and Claudia Thieme for their analytical assisting. This work was funded by the Deutsche Forschungsgemeinschaft (DFG) within the Graduate Research Training Group 1397
‘Regulation of Soil Organic Matter and Nutrient Turnover in Organic Agriculture’ at University of Kassel-Witzenhausen, Germany.
Chapter 3: Carbon and nutrient balances in three mountain oases of Oman
References
Agehara, S. and D. D. Warncke (2005). Soil moisture and temperature effects on nitrogen release from organic nitrogen sources. Soil Science Society of America Journal 69(6): 1844-1855.
Al-Rawahi, M., M. Predotova and A. Buerkert (2012). Gaseous nitrogen and carbon emissions from Al Jabal Al Akhdar oasis systems in northern Oman. Submitted to the Journal of Nutrient Cycling in Agroecosystems (06-01-2012).
Atarashi-Andoh, M., J. Koarashi, S. Ishizuka, K. Hirai (2011). Seasonal patterns and control factors of CO2 effluxes from surface litter, soil organic carbon, and root-derived carbon estimated using radiocarbon signatures. Agricultural and Forest Meteorology 153: 149-158.
Buerkert, A., H. Jahn, S. D. Golombek, M. N. Al-Rawahi and J. Gebauer (2010). Carbon and nitrogen emissions from stored manure and cropped fields in irrigated mountain oases of Oman. Journal of Agriculture and Rural Development in the Tropics and Subtropics 111: 65-73.
Buerkert, A., M. Nagieb, S. Siebert, I. Khan and A. Al-Maskri (2005). Nutrient cycling and field-based partial nutrient balances in two mountain oases of Oman. Field Crops Research 94: 149-164.
Burgos, P., E. Madejón and F. Cabrera (2006). Nitrogen mineralization and nitrate leaching of a sandy soil amended with different organic wastes. Waste Management and Research 24: 175-182.
Cannovo, P., A. Richaume and F. Lafolie (2004). Fate of nitrogen and carbon in the vadose zone: in situ and laboratory measurements of seasonal variations in aerobic respiratory and denitrifying activities. Soil Biology & Biochemistry 36: 463-478.
Cuttle, S. (2002). Nutrient budgets as a tool for researchers and farmers. UK Organic Research 2002, Aberystwyth.
De Neve, S. and G. Hofman (2002). Quantifying soil water effects on nitrogen mineralization from soil organic matter and from fresh crop residues. Biology and Fertility of Soils 35(5): 379-386.
Deng, S. P. and M. A. Tabatabai (2000). Effect of cropping systems on nitrogen mineralization in soils. Biology and Fertility of Soils 31(3): 211-218.
Franzluebbers, A. J. (1999). Microbial activity in response to water-filled pore space of variably eroded southern Piedmont soils. Applied Soil Ecology 11(1): 91-101.
Gee, G. W. and J. W. Bauder (1986). Particle size analysis. In: Klute, A. (Ed.), Methods of soil analysis: part 1. Physical and Mineralogical Methods, 2nd ed. Agron. Monogr.
9. ASA and SSSA, Madison, WI.
Golombek, S. D., J. Gebauer and A. Buerkert (2007). Photosynthetic water-use efficiency of irrigated winter and summer crops in a typical mountain oasis of northern Oman. Journal of Plant Nutrition. Soil Science. 170: 98-105.
Hedlund, A., E. Witter, B. X. An (2003). Assessment of N, P and K management by nutrient balances and flows on peri-urban smallholder farms in southern Vietnam.
European Journal of Agronomy 20: 71-87.
Jarecki, M. K., T. B. Parkin, A. S. K. Chan, J. L. Hatfield and R. Jones (2008).
Greenhouse gas emissions from two soils receiving nitrogen fertilizer and swine manure slurry. Journal of Environmental Quality 37(4): 1432-1438.
Kelting, D. L., J. A. Burger and G. S. Edwards (1998). Estimating root respiration, microbial respiration in the rhizosphere, and root-free soil respiration in forest soils.
Soil Biology and Biochemistry 30(7): 961-968.
Kimetu, J., J. Lehmann, S. Ngoze, D. Mugendi, J. Kinyangi, S. Riha, L. Verchot, J.
Recha and A. Pell (2008). Reversibility of soil productivity decline with organic matter of differing quality along a degradation gradient. Ecosystems 11(5): 726-739.
Kladivko, E. J. and D. R. Keeney (1987). Soil nitrogen mineralization as affected by water and temperature interactions. Biology and Fertility of Soils 5(3): 248-252.
Klein, M. and A. Venezian (1985). The Dubas date tropiduchid, Ommatissus binotatus lybicus, a threat to date palms in Isreal. Phytoparasitica 13(2): 95-101.
Klemmedson, J. O. (1989). Soil organic matter in arid and semiarid ecosystems:
Sources, accumulation, and distribution. Arid Soil Research and Rehabilitation 3(2):
99 - 114.
Kuzyakov, Y. (2002). Separating microbial respiration of exudates from root respiration in non-sterile soils: a comparison of four methods. Soil Biology and Biochemistry 34(11): 1621-1631.
Kuzyakov, Y. (2006). Sources of CO2 efflux from soil and review of partitioning methods.
Soil Biology and Biochemistry 38(3): 425-448.
Kuzyakov, Y. and G. Domanski, G. (2000). Carbon input by plants into the soil. Review.
Journal of Plant Nutrition and Soil Science 163: 421-431.
Chapter 3: Carbon and nutrient balances in three mountain oases of Oman
Kuzyakov, Y. and A.A Larionova (2006). Contribution of rhizomicrobial and root respiration to the CO2 emission from soil (A review). Eurasian Soil Science 39(7):
842-854.
Lang, F. and Kaupenjohann, M. (2004). Trace element release from forest floor can be monitored by ion exchange resin tubes. Journal of Plant Nutrition and Soil Science 167: 177-183.
Luedeling, E., Nagieb, M., Wichern, F., Brandt, M., Deurer, M. and Buerkert, A. (2005).
Drainage, salt leaching and physico-chemical properties of irrigated man-made terrace soils in a mountain oasis of northern Oman. Geoderma 125 (3-4):273-285.
Mikkelsen, R. (2005). Nutrient use efficiency: using nutrient budgets. Western Nutrient Management Conference 6: 2-7.
Mokhtar, A. and S. Al Nabhani (2010). Temperature-dependent development of dubas bug, Ommatissus lybicus (Hemiptera: Tropiduchidae), an endemic pest of date palm, Phoenix dactylifera. Eurpean Journal of Entomology 107: 681-685.
Nagieb, M., J. Häser, S. Siebert, E. Luedeling and A. Buerkert (2004). Settlement history of a mountain oasis in northern Oman - evidence from land-use and archacological studies. Die Erde 135 (1): 81-106.
Nierop, K. G. J., M. M. Pulleman and J. C. Y. Marinissen (2001). Management induced organic matter differentiation in grassland and arable soil: a study using pyrolysis techniques. Soil Biology and Biochemistry 33(6): 755-764.
Nyberg, K., A. Schnürer, I. Sundh, Å. Jarvis and S. Hallin (2006). Ammonia-oxidizing communities in agricultural soil incubated with organic waste residues. Biology and Fertility of Soils 42(4): 315-323.
Ouédraogo, E., A. Mando and N. P. Zombré (2001). Use of compost to improve soil properties and crop productivity under low input agricultural system in West Africa.
Agriculture, Ecosystems and Environment 84(3): 259-266.
Predotova, M., W. Bischoff and A. Buerkert (2011). Mineral nitrogen and phosphorus leaching in vegetable gardens of Niamey, Niger. Journal of Plant Nutrition and Soil Science 174: 47-55.
Predotova, M., J. Gebauer, R.V.C, Diogo, E. Schlecht and A. Buerkert (2010). Gaseous nitrogen and carbon emissions from urban gardens in Niamey, Niger. Field Crops Research 115: 1-8.
Predotova, M., R. Kretschmann, J. Gebauerand A. Buerkert (2011). Effects of cuvette surface material on ammonia, nitrous oxide, carbon dioxide and methane
concentration measurements. Journal of Soil Science and Plant Nutrition 174, 347-349.
Paré, T., E. G. Gregorich and S. Nelson (2000). Mineralization of nitrogen from crop residues and N recovery by maize inoculated with vesicular-arbuscular mycorrhizal fungi. Plant and Soil 218(1): 11-20.
Pumpanen, J., J. Heinonsalo, T. Rasilo, K.-R. Hurme and H. Ilvesniemi (2009). Carbon balance and allocation of assimilated CO2 in Scots pine, Norway spruce, and Silver birch seedlings determined with gas exchange measurements and 14C pulse labelling. Trees - structure and function 23(3): 611-621.
Robinson, C. H. (2002). Controls on decomposition and soil nitrogen availability at high latitudes. Plant and Soil 242(1): 65-81.
Safi, Z., M. Predotova, E. Schlecht and A. Buerkert (2011). Horizontal matter fluxes and leaching losses in urban and peri-urban agriculture of Kabul, Afghanistan. Journal of Plant Nutrition and Soil Science.
Scoones, I. and C. Toulmin (1998). Soil nutrient balances: what use for policy?
Agriculture, Ecosystems and Environment 71: 255-267.
Sheldrick, W.F., J.K. Syers, and J. Lingard (2002). A conceptual model for conducting nutrient audits at national, regional, and global scales. Nutrient Cycling in Agroecosystems. 62(1):61-72.
Siebert, S., M. Nagieb and A. Buerkert (2007). Climate and irrigation water use of a mountain oasis in northern Oman. Agricultural Water Management 89(1-2): 1-14.
Siegfried, K., D. Herbert, E. Schlecht and A. Buerkert (2011). Nutrient and carbon balances in organic vegetable production on an irrigated, sandy soil in northern Oman. Journal of Plant Nutrition and Soil Science: 1-12.
Szili-Kovács, T., K. Török and E.L Tilston (2007). Promoting microbial immobilization of soil nitrogen during restoration of abandoned agricultural fields by organic additions.
Biology and Fertility of Soils 43(6): 823-828.
Watanabe, F. S. and S. R. Olsen. (1965). Test of an ascorbic acid method for determining phosphorus in water and NaHCO3 extracts from soils. Soil Science Society of America Proceedings 29: 677-678.
Werth, M. and Y. Kuzyakov (2008). Root-derived carbon in soil respiration and microbial biomass determined by 14C and 13C. Soil Biology and Biochemistry 40(3): 625-637.
Chapter 3: Carbon and nutrient balances in three mountain oases of Oman
Wichern, F., E. Luedeling, T. Müller, R. G. Joergensen and A. C. Buerkert (2004). Field measurements of the CO2 evolution rate under different crops during an irrigation cycle in a mountain oasis of Oman. Applied Soil Ecology 25: 85-91.
Wichern, F., T. Müller, R. Joergensen and A. Buerkert (2004). Effects of manure quality and application forms on soil C and N turnover of a subtropical oasis soil under laboratory conditions. Biology and Fertility of Soils 39(3): 165-171.
Williams, D. E. (1948). A rapid manometer method for the determination of carbonate in soils. Soil Science Society of America Journal 13: 127-129.
Zaman, M. and S. X. Chang (2004). Substrate type, temperature, and moisture content affect gross and net N mineralization and nitrification rates in Agroforestry systems.
Biology and Fertility of Soils 39(4): 269-279.
Chapter 4. Gaseous nitrogen and carbon emissions from Al Jabal Al Akhdar oasis systems in northern Oman
3Abstract
The effects of temperature, irrigation, and manure quality on gaseous nitrogen (N) and carbon (C) emissions from irrigated agriculture in subtropical high mountain agriculture are poorly investigated. To fill this gap of knowledge, we conducted a study in two oases of different altitudes in Al Jabal Al Akhdar mountains of northern Oman. In 2009 and 2010 goat manure was applied to maize (Zea mays L.) at a typical rate of 29 and 24 t dry matter.ha-1, C/N ratios of 18 and 16, and a total N concentration of 2.4 and 2.2% in Al’Ayn (57o39’30”E, 23o04’10”N, 1,900 m asl) and Masayrat ar Ruwajah (57o40’13”E, 23o02’37”N, 1,030 m asl), respectively. Despite the significantly higher air temperature (P<0.001) during the whole experimental period at the lower oasis, emissions of NH3-N (119 g ha-1 h-1) and N2O-N (184 g ha-1 h-1) were highest at Al’Ayn during the first day after manure application. Subsequently, these emissions decreased very fast and reflected changes in air temperature rather than soil temperature. In contrast, CO2-C emissions were very high throughout the entire experimental period averaging 9.2 and 7.7 kg ha-1 h-1 in Masayrat and Al’Ayn, respectively. Similarly, CH4-C emissions were higher in Masayrat and showed a positive correlation with air temperature (r2=0.647, P<0.001). The higher initial NH3-N and N2O-N emissions in Al’Ayn most likely reflect the higher rate of manure application with higher C/N ratio and total N concentration. Overall the data reflect the high biological activity of the man-made soils in these irrigated agro-ecosystems.
Keywords: Ammonia; carbon dioxide; di-nitrous oxide, gaseous emission; methane;
mountain agriculture.
3 This chapter was submitted on 6.01.2012 as: Al-Rawahi, M.N., Predotova, M, and Buerkert, A. Gaseous nitrogen and carbon emissions from Al Jabal Al Akhdar oasis systems in northern Oman to Nutrient Cycling in Agroecosystems.
Chapter 4: Gaseous nitrogen and carbon emissions from Al Jabal Al Akhdar oasis systems in northern Oman
Introduction
Recently, agro-ecosystem of the ancient arid mountain oases of Oman received increasing attention in order to unravel the causes of their often millennia old sustainable productivity (Golombek et al., 2007; Siebert et al., 2007). Crop rotation, diverse germplasm (Gebauer et al., 2007), high quality irrigation water and a well managed irrigation of man-made soils with superior drainage (Luedeling et al., 2005), and the regular application of large amounts of manure composts are thought to be key features in maintaining soil fertility on the silt-filled terrace fields of these oases (Buerkert et al., 2005). On the other hand these systems are model cases for the role that intensive irrigated agriculture plays in enhancing nitrogen (N) and carbon (C) emissions as ammonia (NH3), nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) to the atmosphere (Cole et al., 1997; Dobbie and Smith, 2001; Velthof et al., 2005; Gregorich et al., 2005; Konda et al., 2008; Predotova et al. 2010). Gaseous N emissons from soils are due to complex microbial processes that are dependent in time and space on a soil’s redox potential, pH, temperature, and microbial processes (Ji and Brune, 2006; Saad and Conrad, 1993; Dobbie and Smith, 2001). Previous studies reported high N2O emissions as a result of denitrification at water filled pores space (WFPS) ≥ 70%, while N2 production was observed at WFPS ≥ 90% (Ruser et al., 2006).
CO2 emissions from agricultural soils are governed by root, microbial and faunal respiration, and by the oxidation of soil organic matter by soil microorganisms. Likewise, CH4 fluxes from agricultural soils depend on the anaerobic decomposition of soil organic matter and the activities of methanogenic and methanotrophic soil microbes (Segers, 1998; Metay et al., 2007; Pozdnyakov et al., 2010)
Due to the typically high manure application rates reflecting the connectedness of agricultural and pastoral components of the landuse systems, Omani oases were described as a temporary nutrient sink (Buerkert et al., 2005). However, little information is available on gaseous losses of C and N under such irrigated subtropical conditions with year-round high temperatures (Wichern et al., 2004). Based on preliminary findings, we hypothesized for this study that across irrigation cycles with resulting changes in soil moisture, gaseous N and C emissions varied strongly with altitude (Buerkert et al., 2010).
Materials and Methods
4.2.1 Site description
The study was conducted along one of the steepest elevation gradients of agriculturally used land on the Arabian Peninsula. We used the two mountain oases of Al'Ayn (57o39’30”E, 23o04’10”N, 1,900 m asl) at the top of the Wadi Muaydin watershed limiting the Sayq Plateau of Al Jabal Al Akhdar (Arabic: ‘Green Mountains’) to the south, and of Masayrat ar Ruwajah (57o40’13”E, 23o02’37”N, 1,030 m asl), the lowest oasis of the watershed. During winter, the minimum air temperature was 1 oC at Al’Ayn and 9 oC at Masayrat, while respective summer maxima were 37 oC and 43 oC. Erratic rainfall is a major factor limiting the sustainability of irrigated agriculture in northern Oman (Luedeling et al., 2005; Luedeling and Buerkert, 2008). Therefore since centuries farmers in these oases irrigate their terraced agricultural area using an Aflaj irrigation system (Arabic: ‘aflaj’ is the plural of ‘falaj’) whose sophisticated management is considered a key factor for the sustainability of agricultural production in Oman (Siebert et al., 2007).
In Al'Ayn agricultural production relies on typical Mediterranean perennials such as pomegranate (Punica garanatum L.), rose (Rosa damascene L.), apricot (Prunus armeniaca L.), peach (Prunus persica L), walnut (Juglans regia L.), apple (Malus domestica L.), plum (Prunus domestica L.), pear (Pyrus communis L.), fig (Ficus carica L.), and grape (Vitis vinifera L.), and on annual crops like garlic (Allium sativum L.), alfalfa (Medicago sativa L.), maize (Zea mays L.), and barley (Hordeum vulgare L.). In Masayrat instead, agriculture is dominated by groves of date palm (Phoenix dactylifera L.), lime (Citrus aurantiifolia L.), sweet lime (Citrus limettioides L.), bitter orange (Citrus aurantium L.) citron (Citrus medica L.) orange (Citrus sinensis L.), lemon (Citrus lemon L.), banana ( Musa x paradisiaca L.), papaya (Carica papaya L.), guava (Psidium guajava L.), and mango (Mangifera indica L.) while annual crops are similar to those in Al'Ayn.
4.2.2 Climatic conditions and soil properties
In both oases experimental data were collected during the summer months (May-September) of 2009 and 2010 in fields prepared to grow fodder maize. For this purpose six fields were selected at each location and prior to measurements of gas emissions four representative samples were collected from the topsoil (0-0.15m) of each field,
Chapter 4: Gaseous nitrogen and carbon emissions from Al Jabal Al Akhdar oasis systems in northern Oman
pooled, air-dried, and sieved to < 2 mm. Soil pH was measured at 1:2.5 soil/water and salinity as electrical conductivity (EC) in a 1:10 soil/water solution (GMH 3410, Greisinger Electronic, Regenstauf, Germany). Soil total N and C were measured by a thermal conductivity detector (Vario MAX CHN Analyser, Elementar Analysensysteme GmbH, Hanau, Germany). The percentage of inorganic soil C (Cinorg) was quantified using a calcimeter as 12% of CaCO3. Soil phosphorous (P) was extracted with NaHCO3
according to Olsen (Watanabe and Olsen, 1965) and measured with a spectrophotometer (U-2000, Hitachi Ltd, Tokyo, Japan). To determine soil potassium (K) concentration, samples were extracted with calcium acetate lactate and extracts measured with a flame photometer (743 AutoCal, Instrumentation Laboratory Co., Bedford, MA, USA).
For the analysis of the effects of elevation on air temperature and relative humidity, the latter were measured at 30 min intervals throughout the research period using Onset Hobo-Pro® climate loggers (Onset Computer Co., Bourne, MA, USA). In addition to these devices Watchdog® weather stations (Spectrum Technologies Inc., Plainfield, IL, USA) were placed at representative locations at Al’Ayn and Masayrat oases to record climatic data throughout the research period.
4.2.3 Application of manure
Before planting of crops, farmers divided their terraced fields into typical 1-6 m2 ridge-surrounded irrigation plots (Arbic: ‘Jalba’) to facilitate flood irrigation and manure application. The amount of dry goat manure applied to each experimental field was 29 t ha-1 in Al’Ayn and 24 t ha-1 in Masayrat. From each oasis six manure samples were collected at application, pooled, dried at 60 oC, ground, and analysed for N, P, K, sodium (Na) and organic carbon (Corg).
4.2.4 Measurements of N and C emissions
As labour constraints did not allow to measure gaseous emissions of NH3-N, N2O-N, CO2-C, and CH4-C in true replicate plots simultaneously over time and space, these were quantified in three plots (sub-samples) of one representative field at each oasis. Consequently relationships between gaseous emissions, soil moisture, and air temperature were reported for each oasis separately. Fluxes were measured using a photo-acoustic infra-red multi-gas analyzer (INNOVA 1312-5, INNOVA AirTech instruments, Ballerup, Denmark) to which a Teflon®-coated cuvette made of a standard
PVC tube with 0.30 m diameter and 0.11 m high was attached (Predotova et al., 2010, 2011). To insure a tight fitting of the cuvette (closed chamber) during measurements intervals, four PVC rings with a diameter of 0.30 m and height of 0.06 m were installed into the ground of each plot to avoid leakage or gas penetration from the outside. Inside of the cuvette a thermo-hygrometer sensor (PCE-313 A, Paper-Consult Engineering Group, Meschede, Germany) allowed to monitor temperature and humidity.
Measurements were carried out on five occasions per day, lasting from 6 am until 8 pm.
Each measurement lasted for two hours (6-8 am, 9-11 am, 12-2 pm, 3-5 pm, and 6-8 pm). All measurements were repeated three times per ring to obtain a total of 12 measurements per occasion. Measurements started immediately after the first irrigation and application of manure and were repeated every day throughout two irrigation cycles.
To quantify the effect of soil moisture content and temperature on gaseous emissions, volumetric water content of the soil was determined at 5 cm depth with a TDR/FDR soil moisture meter (Theta Probe Sensor attached to Infield7b, UMS, Munich, Germany) and soil temperature with a digital thermometer (Carl ROTH GmbH, Karlsruhe, Germany).
4.2.5 Statistical analysis
Data were analyzed with SPSS version 17.0 (SPSS Inc., Chicago, USA), while graphs were made with Sigma Plot 10.0. Normality of data was tested by the Kolmogrov-Smirnov test and climatic differences between the two oases with a t-test at P < 0.05.
Data whose residuals were not normally distributed were log-transformed before statistical analysis was performed. Repeated measures analysis of variance (ANOVA) with Greenhouse-Geisser correction for sphericity was performed for gases at each oasis separately to determine possible trends of emissions over time.
Results
4.3.1 Climatic conditions
Due to the major altitude differences air temperatures at Masayrat were significantly (P<0.001) higher than those at Al’Ayn (Figure 1b) with maximum / minimum values of 37.6°C / 26.3°C and 30.5°C / 23.5°C, respectively. Water availability-dependent average irrigation frequency was 2-3 days at Masayrat and 4-5 days at Al’Ayn. Between irrigation events volumetric soil moisture content varied between 40% after irrigation to 20% before the next event. Wind speed was significantly higher (P<0.001) at Al’Ayn than
Chapter 4: Gaseous nitrogen and carbon emissions from Al Jabal Al Akhdar oasis systems in northern Oman
at Masayrat, reaching respective maxima of 10.6 and 2.2 km h-1 (Figure 1c). On the other hand, relative air humidity was higher (P=0.04) at Masayrat
4.3.2 Soil and manure properties
Soil inorganic carbon (Cinorg) was > 4% in both oases reflecting CaCO3 percentages > 40% (Table 1), and organic carbon (Corg) values were 5.3 and 6.6% in Al’Ayn and Masayrat, respectively. Soil N concentrations and pH values were similar in both oasis soils. Although electrical conductivity (ECo) was higher at Masayrat than at Al’Ayn, the data did not indicate saline conditions. Total N and Corg values in the applied goat manure were higher in Al’Ayn than in Masayrat with C/N ratios varying between 18 and 16 at similar P, K and Na concentrations (Table 2).
Table 1. Soil chemical properties of the selected fields at the oases of Al'Ayn and Masayrat ar Rawajah on Al Jabal Al Akhdar, northern Oman.
Villages EC pH Cinorg CaCO3 Corg N P (Olsen) K
dS/m % % % % P2O5 g/100g mg/g
Al’Ayn 0.15 7.98 5.1 42.6 5.3 0.5 0.032 0.1 Masayrat 0.22 7.95 4.3 40.0 6.6 0.4 0.019 0.2
Table 2. Concentration of carbon (C) and mineral elements in goat manure collected from the oases of Al'Ayn and Masayrat ar Rawajah on Al Jabal Al Akhdar, northern Oman.
Manure N P K Na Corg C/N ratio
--- mg g-1 --- %
Al’Ayn 24 4.4 13.5 2.7 42.8 18
Masayrat 22 4.5 14.3 3.2 36.3 16
Time (days of measurements)
0 1 2 3 4 5 6 7 8 9 10
Relative humidity (RH%)
0 10 20 30 40 50 60
Air RH%-Al'Ayn Air RH%-Masayrat
(d)
Time (days of measurements)
0 1 2 3 4 5 6 7 8 9 10
Wind speed (km/h)
0 2 4 6 8 10 12
Wind speed-Al'Ayn Wind speed-Masayrat
(c)
Time (days of two irrigation cycles)
0 1 2 3 4 5 6 7 8 9 10
Soil moisture content (%)
0 10 20 30 40 50 60 70 80
Soil moisture-Al'Ayn Soil moisture-Masayrat
Soil temperature (oC)
0 5 10 15 20 25 30 35
Soil temperature-Al'Ayn Soil temperature-Masayrat
(a)
Time (days of measurements)
0 1 2 3 4 5 6 7 8 9 10
Air temperature (oC)
10 15 20 25 30 35 40
Air temperature-Al'Ayn Air temperature-Masayrat
(b)
Figure 1. Average soil moisture and temperature at 5 cm depth (a), ambient air temperature (b), wind speed (c) and ambient air relative humidity (RH %; d) during the experimental period (10 days) at the oases of Al'Ayn and Masayrat ar Rawajah, Al Jabal Al Akhdar, northern Oman.
Chapter 4: Gaseous nitrogen and carbon emissions from Al Jabal Al Akhdar oasis systems in northern Oman
4.3.3 Gaseous emissions
In Al’Ayn, fluxes of NH3-N and N2O-N reached maximum values of 119 and 184 g ha-1 h-1 during the first day after manure application, however, thereafter emissions quickly declined (Figure 2). Although N2O-N emissions were enhanced by the second irrigation event on the fourth day, differences were insignificant after the second day. As a result of the difference in flux rates between the first two days and the subsequent ones, NH3-N and N2O-N data were not normally distributed (K-S test, P<0.001) and both periods were thus analyzed separately. Similar trends were determined from Masayrat fields with maximum initial NH3-N emissions of 36 g ha-1 h-1 and N2O-N fluxes of 39 g ha-1 h-1. Annual gaseous N emitted from maize plots in Al’Ayn and Masayrat totaled 225 and 297 kg ha-1 yr-1, respectively.
Throughout the entire experimental period, CO2-C fluxes averaged 7.7 and 9.2 kg ha-1 h-1, whereas CH4-C fluxes averaged 0.11 and 0.17 kg ha-1 h-1 in Al’Ayn and Masayrat.
Consequently, cumulative gaseous C emitted from maize fields in Al’Ayn was 68.4 t ha-1 yr-1 compared to 82.1 t ha-1 yr-1 from Masayrat.
The linear regression analysis revealed that air temperature significantly affected N and C emissions, more than soil moisture in both oases. However, this was not the case for the N2O-N emissions from Al’Ayn (P=0.071). Meanwhile, no significant relationship (P>0.05) was observed between soil temperature and any of the emissions in either oases. During the first two days, NH3-N and N2O-N emissions were positively correlated with soil moisture (r2=0.753, P<0.001), (r2=0.532, P=0.010), respectively. Thereafter, N2O-N emission was weakly correlated with soil moisture (r2=0.128, P=0.020), while the effect of soil moisture on NH3-N emissions was statistically not significant (P=0.282). In contrast, air temperature enhanced fluxes of CO2-C (r2=0.253, P<0.001) and CH4-C (r2=0.154, P=0.005).
In Masayrat, air temperature positively affected N and C emissions, while there was no obvious correlation (P>0.05) with soil moisture. Due to the non-normally distributed residuals, log-transformed NH3-N and N2O-N variables were used to perform regression analysis. The NH3-N, N2O-N, CO2-C, and CH4-C emissions were affected by air temperature (r2=0.407, P<0.001), (r2=0.367, P<0.001), (r2=0.279, P<0.001), and (r2=0.647, P<0.001), respectively.
0 1 2 3 4 5 6 7 8 0
50 100 150 200 250 300 350 0 3000 6000 9000 12000 15000 18000 Al'Ayn
0 20 40 60 80 100 120 140
0 1 2 3 4 5 6 7 8 9
CH4-C emission (g ha-1 h-1 ) 0 50 100 150 200 250 300 350 0 3000 6000 9000 12000 15000 18000
Masayrat ar Rawajah
0 20 40 60 80 100 120 140
Time (day after manure application) 0
50 100 150 200 250
0 50 100 150 200 250
Time (day after manure application) CO2-C emission (g ha-1
-1-1 h-1-1 h)NO-N emission (g ha)NH-N emission (g ha-1h)23
Figure 2. NH3-N, N2O-N, CO2-C and CH4-C emissions from the two oases of Al'Ayn and Masayrat ar Rawajah at Al Jabal Al Akhdar, northern Oman, throughout the research period. Vertical bars indicate standard errors of the means. Arrows indicate irrigation events.
Chapter 4: Gaseous nitrogen and carbon emissions from Al Jabal Al Akhdar oasis systems in northern Oman
Air Temperature (oC)
22 24 26 28 30 32
NH3-N emission (g ha-1 h-1 ) 0 5 10 15 20 25 30 35
Soil moisture content (%)
15 20 25 30 35 40 45
N2O-N emission (g ha-1 h-1 ) 0 20 40 60 80 100
Air Temperature (oC)
22 24 26 28 30 32
CO2-C emission (g ha-1 h-1 ) 0 2000 4000 6000 8000 10000 12000 14000 16000
Air Temperature (oC)
22 24 26 28 30 32
CH4-C emission (g ha-1 h-1 ) 0 50 100 150 200 250
(a) (b)
(c) (d)
y = 0.75 x - 9.385 r2 = 0.128 y = 1.190 x - 18.094
r2 = 0.116
y = 865.07 x - 16027.5
r2 = 0.253 y = 10.142 x - 178.898
r2 = 0.154
Figure 3. Relationship between gaseous emissions of NH3-N, N2O-N, CO2-C, and CH4-C with air temperature and soil moisture at the oasis of Al’Ayn, Al Jabal Al Akhdar, northern Oman, during the experimental period.
Figure 4. Relationship between gaseous emissions of NH3-N, N2O-N, CO2-C, and CH4-C with air temperature and soil moisture at the oasis of Masayrat ar Ruwajah, Al Jabal Al Akhdar, northern Oman, during the experimental period.
Air Temperature (oC)
24 26 28 30 32 34 36 38 40
NH3-N emission (g ha-1 h-1 ) 5 10 15 20 25 30 35 40
Air Temperature (oC)
24 26 28 30 32 34 36 38 40
N2O-N emission (g ha-1 h-1 ) 0 10 20 30 40 50
Air Temperature (oC)
24 26 28 30 32 34 36 38 40
CO2-C emission (g ha-1 h-1 )
6000 7000 8000 9000 10000 11000 12000 13000 14000
Air Temperature (oC)
24 26 28 30 32 34 36 38 40
CH4-C emission (g ha-1 h-1 ) 50 100 150 200 250 300 350 y = 1.445 x - 27.879
r2 = 0.407 y = 1.404 x - 29.447
r2 = 0.367
y = 284.17 x - 209.879
r2 = 0.279 y = 14.875 x - 306.712
r2 = 0.647
(a) (b)
(c) (d)
Chapter 4: Gaseous nitrogen and carbon emissions from Al Jabal Al Akhdar oasis systems in northern Oman
Discussion
4.4.1 NH3-N and N2O-N
Although over the entire experimental period of the first manure application air temperatures were higher at Masayrat than at Al’Ayn, highest emissions of NH3-N (119 g ha-1 h-1) and N2O-N (184 g ha-1 h-1) were recorded at Al’Ayn. While air and soil temperature and soil moisture are certainly the most important factors affecting NH3-N and N2O-N volatilization (Mkhabela et al., 2009), many other factors also determine this process (Mugasha and Pluth, 1995). The higher initial NH3-N and N2O-N emissions in Al’Ayn most likely reflect the higher rate of manure application with higher C/N ratio and total N (24 mg g-1). The high post-application emissions of NH3-N and N2O-N from Al’Ayn probably reflected the high initial NH4+ and NO3- in the applied manure as a consequence of the aerobic microbial activity through ammonification and nitrification (Burger and Jackson, 2003). Breuer et al. (2002) reported that the nitrification process was positively correlated with increasing soil temperature, but negatively affected by increasing soil WFPS. After the initial two days of our experiment, N2O-N emission from Al’Ayn was more affected by soil moisture (r2=0.128, P=0.020), while the effect of soil moisture on NH3-N emissions was statistically not significant (P=0.282). This likely reflects the fact that N2O-N emissions are strongly governed by the soil moisture status (Bateman and Baggs, 2005). In our experiment manure storage may have affected manure quality as farmers in both oases typically store animal faeces in heaps or PE fiber bags laying in the fields until used for the next cropping season. Previous findings (Buerkert et al., 2010) indicated large N and C losses from prolonged field storage of manure under such conditions.
In both oases experimental soils were alkaline thereby enhancing temperature- and moisture-driven NH3 volatilisation (Table1 and 2; Chantigny et al. 2004; Ji and Brune 2006). According to Huijsmans et al. (2001) NH3 volatilization depends on the initial NH4+
content of the manure, application rate, wind speed, air temperature and relative humidity.
4.4.2 CO2-C and CH4-C
In both oases C-fluxes were substantially higher at mid-day than during morning and evening hours, reflecting the direct effect of temperature on the daily release pattern
(Figure 2). As a sequence of the shorter irrigation intervals at Masayrat, soil moisture over time did not differ in both oases even though air temperature was significantly (P<0.001) higher at Masayrat. The high CO2-C flux rates measured at Al’Ayn and Masayrat confirm previous survey results of Buerkert et al. (2010) who determined similar values for irrigated soils of these oases. These C turnover rates are an indicator of microbial activities and root respiration (Dhillion et al., 1995; Kelting et al., 1998;
Kuzyakov and Domanski, 2002) but the high soil carbonate concentrations (CaCO3 or MgCO3) could also have contributed to CO2 emissions.
The measured CH4-efflux reflects the net effect of methanotrophic and methanogenic processes (Whalen and Reeburgh, 1996; Trotsenko et al., 2009) that are governed by the soils’ redox potential. Our results indicated high CH4-C emissions even at low moisture of the surface soil such as at the end of the irrigation cycle. Previous findings underlined the role of anaerobic microsites in soil layers for CH4 production (Smith et al., 2003) and of non-microbial aerobic CH4 emission from dry and fresh organic matter and plant materials (Keppler et al., 2006; Vigano et al., 2008;
Brüggemann et al., 2009). Additional work using isotope signatures may be necessary to understand the pathway of non-microbial aerobic CH4 emissions and their role in irrigated Corg-rich soils such as ours (Vigano et al,. 2009).
Conclusions
Our data provide evidence of the high biological activity of the irrigated Irragric Anthrosols of intensively manured oasis agroecoystems in Oman. Under the given subtropical climate conditions, the turnover of soil organic matter is very fast and leads to large C and N emissions, particularly immediately after the addition of animal manure with a narrow C/N ratio. Our results showed a clear effect of air temperature and soil moisture on N and C fluxes that are modified by the quality and quantity of the applied manure. To better understand the interactions of temperature, moisture and substrate quality in these soils, further studies under controlled conditions are necessary to unravel the turnover processes for the different C and N pools.
Chapter 4: Gaseous nitrogen and carbon emissions from Al Jabal Al Akhdar oasis systems in northern Oman
Acknowledgements
We thank the farmers of Al Jabal Al Akhdar and the Agricultural Extension Centre of the Ministry of Agriculture and Fisheries at Sayh Qatanah (Oman) who supported us in conducting this experiment. We are also grateful to Eva Wiegard and Claudia Thieme for their analytical assistances. The study was funded by the Deutsche Forschungsgemeinschaft (DFG) within the Graduate Research Training Group 1397
‘Regulation of Soil Organic Matter and Nutrient Turnover in Organic Agriculture’ at University of Kassel-Witzenhausen, Germany.
References
Bateman, E. J. and E. M. Baggs (2005). Contributions of nitrification and denitrification to N2O emissions from soils at different water-filled pore space. Biology and Fertility of Soils 41:379-388.
Breuer, L., R. Kiese and K. Butterbach-Bahl (2002). Temperature and moisture effects on nitrification rates in tropical rain-forest soils. Soil Science Society of America 66(3): 834-844.
Brüggemann, N., R. Meier, D. Steigner, I. Zimmer, S. Louis, and J-P. Schnitzler (2009).
Nonmicrobial aerobic methane emission from poplar shoot cultures under low-light conditions. New Phytologist 182(4):912-918.
Buerkert, A., H. Jahn, S. D. Golombek, M. N. Al-Rawahi, and J. Gebauer (2010). Carbon and nitrogen emissions from stored manure and cropped fields in irrigated mountain oases of Oman. Journal of Agriculture and Rural Development in the Tropics and Subtropics 111:65-73.
Buerkert, A., M. Nagieb, S. Siebert, I. Khan and A. Al-Maskri (2005). Nutrient cycling and field-based partial nutrient balances in two mountain oases of Oman. Field Crops Research 94:149-164.
Burger, M. and L. E. Jackson (2003). Microbial immobilization of ammonium and nitrate in relation to ammonification and nitrification rates in organic and conventional cropping systems. Soil Biology and Biochemistry 35(1):29-36.
Chantigny, M. H., P. Rochette, D. A. Angers, D. Masse and D. Cote (2004). Ammonia volatilization and selected soil characteristics following application of anaerobically digested pig slurry. Soil Science Society of America 68:306-312.
Cole, C. V., J. Duxbury, J. Freney, O. Heinemeyer, D. Minami, A. Mosier, A. Paustian, N.
Rosenberg, N. Sampson, D. Sauerbeck and Q. Zhao (1997). Global estimates of potential mitigation of greenhouse gas emissions by agriculture. Nutrient Cycling in Agroecosystems 49:221-228.
Dhillion, S. S., J. Roy, and M. Abrams (1995). Assessing the impact of elevated CO2 on soil microbial activity in a Mediterranean model ecosystem. Plant and Soil 187(2):333-342.
Dobbie, K. E. and K. A. Smith (2001). The effects of temperature, water-filled pore space and land use on N2O emissions from an imperfectly drained gleysol. European Journal of Soil Science 52:667-673.
Chapter 4: Gaseous nitrogen and carbon emissions from Al Jabal Al Akhdar oasis systems in northern Oman
Gebauer, J., E. Luedeling, K. Hammer, M. Nagieb and A. Buerkert (2007). Mountain oases in northern Oman: An environment for evolution and in situ conservation of plant genetic resources. Genetic Resources and Crop Evolution 54(3):465-481.
Gregorich, E. G., P. Rochette, A. J. VandenBygaart and D. A. Angers (2005).
Greenhouse gas contributions of agricultural soils and potential mitigation practices in eastern Canada. Soil and Tillage Research 83(1):53-72.
Golombek, S. D., J. Gebauer and A. Buerkert (2007). Photosynthetic water-use efficiency of irrigated winter and summer crops in a typical mountain oasis of northern Oman. Journal of Soil Science and Plant Nutrition 170:98-105.
Huijsmans, J. F. M., J. M. G. Hol and M. M. W. B Hendriks (2001). Effect of application technique, manure characteristics, weather and field conditions on ammonia volatilization from manure applied to grassland. NJAS - Wageningen Journal of Life Sciences 49(4):323-342.
Ji, R. and A. Brune (2006). Nitrogen mineralization, ammonia accumulation, and emission of gaseous NH3 by soil-feeding termites. Biogeochemistry 78(3):267-283.
Kelting, D. L., J. A. Burger and G. S. Edwards (1998). Estimating root respiration, microbial respiration in the rhizosphere, and root-free soil respiration in forest soils.
Soil Biology and Biochemistry 30(7):961-968.
Keppler, F., J. T. G Hamilton, M. Braß and T. Rockmann (2006). Methane emissions from terrestrial plants under aerobic conditions. Nature 439(7073):187-191.
Konda, R., S. Ohta, S. Ishizuka, S. Arai, S. Ansori, N. Tanaka and A. Hardjono (2008).
Spatial structures of N2O, CO2 and CH4 fluxes from Acacia mangium plantation soils during a relatively dry season in Indonesia. Soil Biology & Biochemistry 40:3021-3030.
Kuzyakov, Y. and G. Domanski (2002). Model for rhizodeposition and CO2 efflux from planted soil and its validation by 14C pulse labelling of ryegrass. Plant and Soil 239:87-102.
Luedeling, E., M. Nagieb, F. Wichern, M. Brandt, M. Deurer and A. Buerkert (2005).
Drainage, salt leaching and physico-chemical properties of irrigated man-made terrace soils in a mountain oasis of northern Oman. Geoderma 125:273-285.
Luedeling, E. and A. Buerkert (2008). Effects of land use changes on the hydrological sustainability of mountain oases in northern Oman. Plant and Soil 304:1-20.
Metay, A., R. Oliver, E. Scopel, J.M. Douzet, J. Aloisio Alves Moreira, F. Maraux, B.J.
Feigl and C. Feller (2007). N2O and CH4 emissions from soils under conventional
and no-till management practices in Goiânia (Cerrados, Brazil). Geoderma 141(1-2):78-88.
Mkhabela, M. S., R. Gordon, D. Burton, E. Smith and A. Madani (2009). The impact of management practices and meteorological conditions on ammonia and nitrous oxide emissions following application of hog slurry to forage grass in Nova Scotia.
Agriculture, Ecosystems and Environment 130(1-2):41-49.
Mugasha, A. G. and D. J. Pluth (1995). Ammonia loss following surface application of urea fertilizer to undrained and drained forested minerotrophic peatland sites in central Alberta, Canada. Forest Ecology and Management 78(1-3):139-145.
Predotova, M., J. Gebauer, R. V. C. Diogo, E. Schlecht and A. Buerkert (2010). Gaseous nitrogen and carbon emissions from urban gardens in Niamey, Niger. Field Crops Research 115:1-8.
Predotova, M., R. Kretschmann, J. Gebauer and A. Buerkert (2011). Effects of cuvette surface material on ammonia, nitrous oxide, carbon dioxide and methane concentration measurements. Journal of Soil Science and Plant Nutrition 174:347-349.
Pozdnyakov, L., A. Stepanov and N. Manucharova (2010). Anaerobic methane oxidation in soils and water ecosystems. Moscow University Soil Science Bulletin 66(1):24-31.
Ruser, R., H. Flessa, R. Russow, G. Schmidt, F. Buegger and J. C. Munch (2006).
Emission of N2O, N2 and CO2 from soil fertilized with nitrate: effect of compaction, soil moisture and rewetting. Soil Biology and Biochemistry 38:263-274.
Saad, O. A. L. O. and R. Conrad (1993). Temperature dependence of nitrification, denitrification and turnover of nitric oxide in different soils. Biology and Fertility of Soils 15:21-27.
Segers, R. (1998). Methane production and methane consumption: a review of processes underlying wetland methane fluxes. Biogeochemistry 41:23-51.
Siebert, S., M. Nagieb and A. Buerkert (2007). Climate and irrigation water use of a mountain oasis in northern Oman. Agricultural Water Management 89(1-2):1-14.
Smith, K. A., T. Ball, F. Conen, K. E. Dobbie, J. Massheder and A. Rey (2003).
Exchange of greenhouse gases between soil and atmosphere: interactions of soil physical factors and biological processes. European Journal of Soil Science 54(4):779-791.